For packaging of integrated circuit chips (especially high power chips), the ability to dissipate heat effectively away from the chip and out of the packaging module is very important. The ability of the module to dissipate heat generated by the chip(s) is generally a function of the quality of the primary heat dissipation path from the chip to the external surface of the module.
In module designs such as those described in U.S. Pat. No. 5,396,403, thermal paste or some other thermally conductive compliant material is used at a point in the primary heat dissipation path from the chip to the external surface of the module. Interfaces (where heat has to cross from one material to another) are generally the weakest link in the heat dissipation path (i.e., they have significantly lower thermal conductivity than other components of the heat dissipation path), even when they are filled with thermally conductive compliant materials.
Some of the advantages of module designs utilizing thermally conductive compliant materials are that the materials have the ability to accommodate statistical variations in thickness of chips to be housed in the module, height of the solder connections (in the case of flip chips packaging), lid cavity depth, thickness of the seal, substrate camber, etc. The ability to control variations in the various component dimensions is difficult, especially where the components may come from different manufacturers or where reworking or modification of components may be required. This problem is especially apparent where large scale commercial production is involved (i.e., a high throughput of modules).
Thus, there is a desire to further improve the thermal performance of electronic package modules in an economical way.